Crankcase Ventilation: Operation
OPERATION
There are two sides to the Positive Crankcase Ventilation (PCV) system. The dirty side of the system consists of the PCV Valve, installed on the Valve Cover Oil Separator, and the PCV Tube that connects between the PCV Valve and Intake Manifold. The clean air side of the system consists of the Make-Up Air (MUA) Tube that connects between the MUA Oil Separator in the Valve Cover and the Fresh Air Hose, and Crankcase Pressure Sensor.
NATURALLY ASPIRATED OPERATION
When the engine is running Naturally Aspirated, clean air flows from the Fresh Air Hose, through the MUA Tube and MUA Oil Separator, to the crankcase. The crankcase vapors are pushed into the other Oil Separator in the Valve Cover. Engine vacuum draws the vapors into the Intake Manifold through the PCV Valve and PCV Tube where they are burned.
The PCV Valve contains a spring loaded plunger. The plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.
Shown below are the typical views of the PCV Valve operation.
When the engine is not operating or during an engine backfire, the spring forces the plunger back against the seat. This prevents vapors from flowing through the valve.
When the engine is at idle or cruising, high manifold vacuum is present. At these times manifold vacuum is able to completely compress the spring and pull the plunger to the top of the valve. In this position there is minimal vapor flow through the valve.
During periods of moderate intake manifold vacuum the plunger is only pulled part way back from the inlet. This results in maximum vapor flow through the valve.
The Crankcase Pressure Sensor is used to diagnose a disconnect in the MUA Tube. The Crankcase Pressure Sensor connects to a fitting on the Clean Air Tube that is also connected to the MUA Tube. The Powertrain Control Module (PCM) monitors the pressure pulsations in the Crankcase Pressure Sensor signal to determine whether or not the hose is connected.